The relationship between amino acid substitutions and electrophoretic mobility changes in proteins will be investigated experimentally using a variety of purified proteins. The procedure of Ferguson plot analysis will be used to separate change and size-shape changes in proteins. The work will also involve Ferguson plot analysis of approximately 50 strains of Drosophila pseudoobscura for ten or more protein producing loci that are known to be polymorphic for electrophoretic mobility. At least five monomorphic loci will also be analyzed in the same strains. The work should contribute information that will be useful in determining whether or not observed electrophoretic mobility differences involve conformational or shape changes. The results will also be used to analyze goodness-of-fit to predictions of models that assume no selective difference between alternative alleles at protein producing loci.